"Bring baggies to bring snacks on your days off the ship "
Absolutely NOT permitted at most ports - you will see notices in your daily bulletin to not take food off the ship. This is a rule of the country you are visiting, not the cruiseline. If caught, your food will be confiscated and you may be fined. Fruit, meat, cheese, etc., are especially verboten.
Prepackaged snacks (boxed cereal, granola bars, etc.) are permitted.